void main () {
  print('hello dart');
  var b = int.parse('3');
  var c = 4;
  var d = b + c;
  print(d);

  List arr = ['zhang san', 'lisi', 'wangsan'];

  String getInfo (String user, [String age = '30']) {
    return '$user --- $age';
  }

  for (int i = 0; i < arr.length; i ++) {
    print(arr[i]);
  }
  print('-------');
  print(getInfo('zhangsan', '30'));
}